JP6601283B2 - Fuel tank - Google Patents

Description

  The present invention relates to a fuel tank.

  Conventionally, Pb—Sn alloy-plated steel sheets that have been used as fuel tank materials have been used habitually because of their excellent properties (for example, workability, tank inner surface corrosion resistance, solderability, seam weldability, etc.). However, with the recent increase in recognition of the global environment, the trend toward Pb-free is being made.

A typical fuel tank material replacing the Pb-Sn alloy-plated steel sheet is a molten Sn-Zn-plated steel sheet. In the following Patent Documents 1 to 3, a molten Sn-Zn-plated steel sheet with a controlled plating structure is used. It is disclosed. More specifically, the following Patent Document 1 discloses a Sn—Zn plated steel sheet in which the Zn content is increased to 60% by mass, and the following Patent Document 2 has a Zn content of 30% by mass. An Sn-Zn plated steel sheet with a% increase is disclosed. Patent Document 3 below discloses a Sn—Zn-plated steel sheet in which the Zn content is increased to 30% by mass, and the major axis of zinc crystals is 250 μm or more, 20 or less / 0.0. It is stated that good corrosion resistance is exhibited by controlling to 25 mm ² .

  Furthermore, as an example of utilizing plating with a large amount of Zn, the following Patent Document 4 discloses a Zn—Ni plated steel sheet in which cracks on the plating surface are controlled, and the following Patent Document 5 discloses zinc-based plating. A steel plate for a fuel tank having a resin film formed thereon is disclosed.

  Moreover, the example using the stainless steel plate excellent in corrosion resistance is disclosed by the following patent document 6, and the example using the steel plate which gave Sn-Zn plating with respect to stainless steel is disclosed by the following patent document 7. .

JP-A-8-269733 JP-A-8-269734 JP-A-8-269735 JP-A-9-241886 JP 2001-341228 A JP 2006-22352 A JP 2009-68102 A

  When the fuel tank is used in a general environment, sufficient performance can be obtained by using a conventionally proposed steel plate.

  However, the inventors have found that the corrosive conditions are more severe than the general environment, such as when externally introduced factors that make the corrosive environment in the fuel tank very severe, such as extremely deteriorated fuel or sludge. Focusing on the case where the action of, acted further.

  The sludge here is a mixture of iron rust and gasoline decomposition products accumulated at the bottom of a gasoline storage underground tank installed at a gas station or the like. Such sludge rises when refueling an underground storage tank with a tank lorry or the like, and the raised sludge may be mixed into a fuel tank of an automobile. When sludge enters the fuel tank of an automobile, an oxygen concentration cell is formed under the sludge, and the (corrosion) corrosion environment becomes severe.

  According to such a study, in order to suppress pitting corrosion, when the factor that makes the corrosive environment in the fuel tank extremely severe such as extremely deteriorated fuel or sludge enters from the outside, the acid component should be reduced. It is important to neutralize and make the corrosive environment in the tank mild.

From the above viewpoint, when the above Patent Document 1 to Patent Document 7 were examined, the following findings could be obtained.
That is, the plated steel sheets disclosed in Patent Document 1 to Patent Document 3 have a small amount of Zn contained in the plating, so that the neutralization of the acid component is insufficient and causes corrosion of the ground iron. Therefore, it is not suitable for the above purpose.

  On the other hand, when utilizing a large amount of Zn as disclosed in Patent Document 4 and Patent Document 5, the neutralization reaction of the acid component is sufficient, but the fuel in the tank is reduced and the steel plate is reduced. When exposed to air, the oxidation of Zn proceeds to produce a large amount of corrosion products, which may lead to problems such as pump clogging.

  Moreover, even if it is a case where the stainless steel plate described in the said patent document 6 and the patent document 7 is used, sufficient characteristic is not exhibited for the rust induction | guidance | derivation under sludge.

  Therefore, the present invention has been made in view of the above problems, and the object of the present invention is good even when a factor that makes the corrosive environment in the fuel tank extremely severe enters from the outside. An object of the present invention is to provide a fuel tank that exhibits corrosion resistance and can suppress the formation of corrosion products due to plating wear.

The gist of the present invention is as follows.
(1) having a plating layer made of Sn-based plating having a composition of Sn- (5 to 40% by mass) Zn or Al-based plating having a composition of Al- (8 to 12% by mass) Si, A fuel tank made of a plated steel sheet having a plating layer adhesion amount of 20 to 50 g / m ² ;
At the bottom of the fuel tank, it is located on the plating layer on the inner surface side of the fuel tank and contains at least one of Zn, Mg, or Zn—Mg alloy, and is given by the following formula (1) A bottom member having a K value of K ≧ 0.030;
A fuel tank.
K = Zn (g) /65.4+Mg (g) /24.3 ... Formula (1)
Here, in the above formula (1),
Zn (g): Zn content in the bottom member (unit: g)
Mg (g): Mg content in the bottom member (unit: g)
It is.
(2) The fuel tank according to (1), wherein the contents of Ni, Fe, Co, and Cu in the bottom member are each 0.5% by mass or less.
(3) On the plated steel sheet and the bottom member, a film layer mainly composed of Cr ³⁺ and having an adhesion amount of 5 to 40 mg / m ² in terms of Cr, or Ti, Zr, P, Ce, Si, Al, or The fuel tank according to (1) or (2), further comprising a chemical conversion treatment layer containing at least one of Li as a main component and not containing chromium and having an adhesion amount of 10 to 1000 mg / m ² .

  As described above, according to the present invention, even when a factor that makes the corrosive environment in the fuel tank extremely severe enters from the outside, it exhibits good corrosion resistance and generates corrosion products due to plating wear. Can be suppressed.

It is the graph which showed the relationship between the adhesion amount of electro Zn plating, and the pitting depth. It is the graph which showed the relationship between the adhesion amount of electric Zn plating, and the amount of corrosion products. It is the graph which showed the relationship between the adhesion amount of electric Zn-Ni plating, and a pitting corrosion depth. It is the graph which showed the relationship between the adhesion amount of electric Zn-Ni plating, and the amount of corrosion products. It is the graph which showed the relationship between the composition and adhesion amount of Sn-Zn plating, and pitting corrosion depth. It is the graph which showed the relationship between the composition and adhesion amount of Sn-Zn plating, and the amount of corrosion products. It is the graph which showed the relationship between the composition and adhesion amount of Al-Si plating, and pitting depth. It is the graph which showed the relationship between the composition and adhesion amount of Al-Si plating, and the amount of corrosion products. It is the graph which showed the relationship between K value according to the Zn amount to give, Mg amount, and Zn-50 mass% Mg amount, and pitting corrosion depth.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

(About examination by the present inventors)
Prior to the description of the fuel tank according to the embodiment of the present invention, the studies performed by the present inventors will be described in detail.

  As a result of detailed investigations on the corrosion phenomenon in the fuel tank, the present inventors have found that the most severe corrosive environment in the fuel tank is that the water caused by condensation is accumulated at the bottom of the tank, and deteriorated fuel or It became clear that it was a case where sludge was mixed. When the deteriorated fuel is mixed in the fuel tank, the organic acid contained in the deteriorated fuel is transferred into the dewed water to become an organic acid aqueous solution having a low pH, which corrodes the plating and the steel plate. Further, when sludge is mixed into the fuel tank, the pH is locally lowered by forming an oxygen concentration cell under the sludge, thereby inducing corrosion. Accordingly, it is important to sufficiently bring Zn or the like, which is an element that neutralizes acid, into the bottom of the tank to suppress perforation.

  On the other hand, locations other than the bottom of the tank where water does not accumulate are exposed to the atmosphere when the fuel is reduced. Therefore, in plating containing a large amount of Zn, the oxidation reaction of Zn by air proceeds and a corrosion product mainly composed of ZnO is generated. Therefore, there is a high possibility that the corrosion product clogs the filter installed at the fuel inlet in the fuel tank and induces a trouble that the engine stops.

  Therefore, in a state where water due to condensation is accumulated at the bottom of the tank and where deteriorated fuel or sludge is mixed from the outside, the tank where the corrosion liquid is accumulated using only a single plated steel sheet as it is. It can be said that it is difficult to manufacture a tank having sufficient compatibility with both the bottom and the vertical wall and ceiling exposed to the atmosphere.

  As a means for solving the above two trade-off problems, the present inventors have shown that the tank body exhibits sufficient corrosion resistance in a general environment and is corroded even when exposed to the atmosphere. Regarding the tank bottom where the corrosive environment becomes severe by using plating that does not produce a large amount of product, it has been conceived that a bottom member containing a substance that alleviates the corrosiveness of accumulated water is separately disposed on the plating. As a result, it is possible to provide a fuel tank with good drilling resistance and corrosion product resistance that exhibits good drilling resistance even in a harsh environment at the bottom of the tank and can suppress the formation of corrosion products. It becomes possible.

<Examination of plating type of plated steel sheet used as material>
Based on the above knowledge, the present inventors have further examined the plating type applied to the plated steel sheet used as the material for the fuel tank.
In the following, first determine the plating type that shows sufficient corrosion resistance in a general corrosive environment and does not generate a large amount of corrosion products even when the fuel in the tank is reduced and exposed to the atmosphere. The following verification was conducted for the purpose.

  The steel plate used as a base material is an IF steel plate (Interstitial free steel plate) excellent in workability, and is a plating type generally used in the market as a tank material, which is an electric Zn plating, an electric Zn-Ni plating, a molten Al-Si. Evaluation was performed by the following method using each of plating and molten Sn—Zn plating.

Electro-Zn plating fixed the composition to 100% by mass of Zn, and electro-Zn—Ni plating fixed the composition to Zn-12% by mass of Ni (that is, containing 12% by mass of Ni, the balance being Zn and impurities) The amount of plating adhesion was changed in the range of 10 to 60 g / m ² per side.

In addition, the molten Sn—Zn plating changes the Zn content in the range of 0 to 50% by mass, the remainder other than Zn is Sn and impurities, and the molten Al—Si plating has an Si content of 0 to 20%. The amount of plating was changed in the range of 10 to 60 g / m ² per one side, with the balance other than Si being changed to Al and impurities in the range of mass%.

Using a treatment liquid mainly composed of Cr ³⁺ such as Cr nitrate and containing ascorbic acid, water-dispersible silica and phosphoric acid, the treatment liquid is applied to the surface of each of the above plated steel sheets, and the amount of Cr equivalent adhesion is on one side. 20 mg / m ² per unit, after drying, Cr: Si: P in the film was applied with a bar coater so that the mass ratio was 1: 3: 2, and then dried at an ambient temperature of 240 ° C. As a result, a film mainly composed of Cr ³⁺ was formed on the surface of each plated steel sheet. Then, the characteristic was evaluated about each obtained plated steel plate.

  Each plated steel sheet prepared as described above was formed into a cylindrical cup shape of 50 mmφ. In addition, a deteriorated gasoline treated by a deterioration method in accordance with JIS K2287 is prepared, 10% by volume of water is added to the deteriorated gasoline, and the lower phase side (water phase side) separated into two phases is separated by a formic acid concentration. It was 100 mg / L, and it adjusted using the reagent so that an acetic acid density | concentration might be 200 mg / L, and it was set as the deteriorated fuel. Thereafter, the obtained deteriorated fuel was sealed in the molded cylindrical cup. The enclosed deteriorated fuel contained 45 cc of deteriorated gasoline and 5 cc of water, and the amount of the deteriorated fuel enclosed was about 80% of the volume of the cylindrical cup.

  The cylindrical cup filled with the deteriorated fuel was left to stand at 45 ° C. for 1000 hours, and the erosion depth after 1000 hours was measured by measuring the focal depth distance using an optical microscope.

  Moreover, in order to evaluate corrosion-resistant product property, after enclosing the deterioration gasoline and water which deteriorated on the same conditions as the above, it left still at 45 degreeC for 50 hours. Thereafter, 40 cc of the deteriorated fuel inside was taken out of the cup, and the vertical wall portion of the cup was exposed to the atmosphere, and further allowed to stand at 45 ° C. for 200 hours. When 200 hours had passed, 40 cc of deteriorated fuel was added so as to be equal to the initial amount. In this state, the mixture was further allowed to stand at 45 ° C. for 50 hours, and thereafter, the internal fuel was reduced in the same manner as in the previous time, and further allowed to stand at 45 ° C. for 200 hours. These operations were repeated four times, and the test was terminated when the total standing time reached 1000 hours.

  After completion of the test, the corrosion products floating in the corrosive liquid and the corrosion products adhering to the inner surface of the cup were weighed. Corrosion products in the corrosive liquid were weighed by filtering the deteriorated fuel with polytetrafluoroethylene (PTFE) filter paper. Moreover, the corrosion product adhering to the inner surface of the cup was weighed after carefully peeling with a vinyl scrubber.

  Furthermore, for the purpose of confirming the amount of corrosion products in which filter clogging occurs in the fuel tank, a 40 liter simulated fuel tank having an average size is manufactured using each of the above plated steel sheets, and fuel ( 35 liters of deteriorated gasoline) was added, and fuel (deteriorated gasoline) was circulated using a pump. The sucked fuel was returned to the tank again, and the sucked amount was measured with a flow meter. Zinc corrosion products were added to the deteriorated fuel in increments of 5 g, and the amount of corrosion products that reduced pump suction was confirmed.

  When 80 g of the corrosion product was added, the pump suction started to decrease, and when 90 g of the corrosion product was added, the pump suction was reduced to less than half. Therefore, it has been confirmed that by making the corrosion product in the tank 80 g or less, there is no adverse effect on the fuel suction. The amount of the corrosion product corresponds to 0.1 g in the 50 mmφ cylindrical cup containing 50 cc of fuel prepared this time.

  Results of the inner surface corrosion resistance test using such a 50 mmφ cylindrical cup are shown in FIGS. 1A to 4B.

FIG. 1A and FIG. 1B are test results for electro-Zn plating.
As is clear from FIG. 1A, the pitting depth is 20 μm or more at any deposition amount, and as is clear from FIG. 1B, the corrosion product is 0. 0 per cup at any deposition amount. It was 1 g or more, and the characteristics were insufficient.

FIG. 2A and FIG. 2B are test results for electrical Zn—Ni plating.
As is clear from FIG. 2A, the pitting resistance is improved by securing the adhesion amount of 20 g / m ² or more per side. On the other hand, as is apparent from FIG. 2B, by setting the adhesion amount to 20 g / m ² or more, a corrosion product due to Zn was produced in an amount of 0.1 g or more per cup.

  From the results shown in FIG. 1A to FIG. 2B, the present inventors show sufficient punching resistance in a general deteriorated fuel environment when electric Zn plating or electric Zn—Ni plating is used, It was concluded that it was difficult to maintain good corrosion resistance properties.

FIG. 3A and FIG. 3B are test results for molten Sn—Zn plating.
As is clear from FIG. 3A, when the adhesion amount of the molten Sn—Zn plating is 20 g / m ² or more per side and the Zn content in the molten Sn—Zn plating is 5 mass% or more, it is good. Pitting corrosion resistance was obtained. On the other hand, as apparent from FIG. 3B, even when the adhesion amount of molten Sn—Zn plating is 20 g / m ² or more per side, the Zn content in molten Sn—Zn plating exceeds 40% by mass. As a result, 0.1 g or more of corrosion products were produced per cup. From the above results, in the molten Sn—Zn plated steel sheet, in order to show sufficient punching resistance in a general deteriorated fuel environment and maintain good corrosion resistance, the Zn content is set to 5 to 5. It has been found that it is important to control the amount within a range of 40% by mass and to secure an adhesion amount of 20 g / m ² or more per side.

4A and 4B show test results for hot-dip Al—Si plating.
As is clear from FIG. 4A, when the adhesion amount of molten Al—Si plating is 20 g / m ² or more and the Si content in molten Al—Si plating is in the range of 0 to 20% by mass, it is good. It showed perforation resistance. Further, as is clear from FIG. 4B, the corrosion resistance property was good in all compositions and plating coverage areas tested. From the above results, in the molten Al-Si plated steel sheet, in order to show sufficient punching resistance in a general deteriorated fuel environment and maintain good corrosion resistance, the Si content is set to 0 to 0. It was found that it is important to control the amount within a range of 20% by mass and to secure an adhesion amount of 10 g / m ² or more per side.

<About workability>
Next, with respect to the molten Sn—Zn plating and the molten Al—Si plating that showed sufficient corrosion resistance in a general deteriorated fuel environment as described above, the workability of plating was confirmed by the following method.

With a general hydraulic forming tester, a forming test was performed using a cylindrical punch having a diameter of 50 mm and a wrinkle suppression pressure of 500 kg / cm ² and a drawing ratio of 2.3.

In both cases of hot Sn—Zn plating and hot Al—Si plating, when the adhesion amount exceeded 50 g / m ² , cracks occurred in the plating layer, and in some cases, the plating also peeled off.

Regarding the plating composition, in the case of molten Sn—Zn plating, good workability was obtained in all composition regions by controlling the adhesion amount to 50 g / m ² or less per side. On the other hand, in the case of molten Al—Si plating, good workability was obtained when the Si content was in the range of 6 to 12% by mass, but cracks occurred in the plating layer outside this content range. When the Si content is as low as less than 6% by mass, it has been clarified that the Fe—Al—Si alloy phase grows thick at the steel plate / plating interface and cracks originate from the grown alloy phase. Moreover, when the Si content was as high as 12% by mass or more, it became clear that cracks were generated through the coarsely precipitated Si phase.

From the above results, in order to show sufficient drilling resistance in a general deteriorated fuel environment, maintain good corrosion resistance property properties, and obtain good workability in a molten Sn-Zn plated steel sheet It was found that it is important to control the Zn content in the range of 5 to 40% by mass and to adjust the adhesion amount to 20 g / m ² or more and 50 g / m ² or less per side. In addition, in the molten Al-Si plated steel sheet, in order to show sufficient drilling resistance in a general deteriorated fuel environment, maintain good corrosion resistance, and obtain good workability, It has been found that it is important to control the amount in the range of 6 to 12% by mass and to make the adhesion amount 20 g / m ² or more and 50 g / m ² or less per side.

<Corrosion resistance under inferior conditions>
Next, in the market using a molten Sn-Zn plated steel sheet and a molten Al-Si plated steel sheet that can withstand processing and have sufficient punching resistance and corrosion product resistance in a general deteriorated fuel environment. The conditions under which sufficient corrosion resistance was obtained under the severe corrosion environment that occurred were confirmed by the following method.

  In the same manner as described above, a plated steel plate was formed into a cylindrical cup shape of 50 mmφ, and a deteriorated gasoline obtained by treating gasoline with a deterioration method based on JISK2287 was prepared inside the obtained cup.

  10% by volume of water is added to the above deteriorated gasoline, and the formic acid concentration becomes 1000 mg / L and the acetic acid concentration becomes 2000 mg / L on the lower phase side (aqueous phase side) separated into two phases. As described above, a highly deteriorated fuel was prepared using a reagent. Thereafter, the obtained highly deteriorated fuel was sealed in the molded cylindrical cup in the same manner as described above. The enclosed highly deteriorated fuel contains 45 cc of gasoline and 5 cc of water.

  The tank filled with the above highly deteriorated fuel was left to stand at 45 ° C. for 1000 hours, and the pitting corrosion depth after 1000 hours was measured in the same manner as described above. As a result, in both the molten Sn—Zn plated steel sheet and the molten Al—Si plated steel sheet, good corrosion resistance cannot be obtained regardless of the amount of adhesion and the plating composition, and pitting corrosion of 20 μm or more is observed under all conditions. Occurred.

  Therefore, in order to milden the corrosive environment inside the tank, the addition of a metal that neutralizes the acid component by reacting with formic acid and acetic acid, which are gasoline degradation products, was investigated. Specifically, Zn, Al, Mg, Ni, Cu, Sn, Cr, Co is selected as a candidate for such a metal, and a small block obtained by cutting out a certain amount from the metal ingot is made in the same manner as described above. The bottom surface of the molded 50 mmφ cylindrical cup was adhered to the bottom surface of the cup with a resin so as to be located in the aqueous phase. Thereafter, in the same manner as described above, 5 cc of water was added to 45 cc of the deteriorated gasoline, and the two-phase separated aqueous phase side was adjusted so that the formic acid concentration was 1000 mg / L and the acetic acid concentration was 2000 mg / L. , And adjusted using reagents.

After holding at 45 ° C. for 1000 hours, the pitting depth was measured in the same manner as described above. The obtained results are shown in FIG.
When using a Zn alone, Mg alone, or a Zn-50 mass% Mg alloy, and bonding and fixing a small block adjusted so that the K value shown in the following formula (1) satisfies K ≧ 0.0015 It was confirmed that pitting corrosion was suppressed. Moreover, about the systematic form of the small block to be provided, Zn alone, Mg alone, or both Zn and Mg are given simultaneously, or a Zn-Mg alloy (Mg content in the alloy is 50% by mass) Even if it is a value other than), there is no difference in effect, and if K ≧ 0.0015 is satisfied, pitting corrosion is suppressed and good corrosion resistance can be secured.

    K = Zn (g) /65.4+Mg (g) /24.3 ... Formula (1)

  Here, in the above formula (1), Zn (g) is the Zn content (unit: g) in the bottom member, and Mg (g) is the Mg content (unit: g) in the bottom member. is there. Further, as apparent from the above formula (1), the K value corresponds to the total number of moles of Zn and Mg contained in the bottom member.

  The upper limit of the K value given by the above formula (1) is not particularly specified, and the larger the value, the better. However, from the viewpoint of cost and weight, about 1 mol / tank is actually the upper limit. As appropriate. The range of K value is more preferably 0.030 to 0.10 mol / tank from the viewpoint of economy.

  Moreover, about Al, Ni, Cu, Sn, Cr, Co other than Zn and Mg, it was not possible to obtain good corrosion resistance in a poor environment.

  Moreover, the following knowledge was able to be acquired regarding the other component contained in Zn, Mg, and a Zn-Mg alloy from the result of having performed this test in parallel. That is, with respect to Ca, Si, Ti, Cr, and Sn, even if they are contained as impurities, the performance was hardly affected. On the other hand, with respect to Ni, Fe, Co, and Cu, these metals deteriorate the corrosion resistance, and it has become clear that it is important to suppress the content to 0.5% by mass or less.

<Corrosion resistance when mixed with sludge>
Next, the following verification was performed for the purpose of simulating corrosion when sludge was mixed. That is, after adjusting with the reagent so that the formic acid concentration in the above-mentioned aqueous phase was 100 mg / L and the acetic acid concentration was 200 mg / L, 1 g of FeOOH as a reagent was added for the purpose of simulating sludge.

  The added FeOOH was dispersed throughout the aqueous phase. Pitting corrosion after 1000 hours at 45 ° C. was investigated in the same manner as described above. As a result, similar to the conditions in which the formic acid concentration was adjusted to 1000 mg / L and the acetic acid concentration was 2000 mg / L on the aqueous phase side, Zn, Mg, or a Zn—Mg alloy was used, and the formula ( It was confirmed that the pitting corrosion was suppressed when the small piece block adjusted so that the K value shown in 1) satisfies K ≧ 0.0015 was adhered and fixed.

Next, the correspondence between various knowledge obtained by the above verification and the actual tank was confirmed.
For a simulated fuel tank with an internal capacity of 40 liters made of Sn-10 mass% Zn-plated steel sheet with an adhesion amount of 30 g / m ² that showed good characteristics in the cup test, Zn, Mg and Zn-Mg alloy were added to the tank bottom. Bonded and fixed under various conditions. In addition, 38 liters of deteriorated gasoline and 100 cc of water treated by a deterioration method in accordance with JISK2287 are prepared, and the reagent is used so that the formic acid concentration in the aqueous phase is 1000 mg / L and the acetic acid concentration is 2000 mg / L. Adjusted to make highly deteriorated fuel. Thereafter, the obtained highly deteriorated fuel was sealed in the molded simulated fuel tank. It left still at 45 degreeC for 1000 hours, and pitting corrosion depth after 1000 hours was measured like the above. As a result, it was found that if the K value represented by the formula (1) satisfies K ≧ 0.030, pitting corrosion can be suppressed and good corrosion resistance can be secured.

  Confirming with respect to the amount of Zn, Mg and Zn—Mg alloy to be applied and the amount of water mixed in the system, K = 0.030 shown in the formula (1) obtained in the actual tank is the value K of the cup test. = 20.times.0.0015, which was confirmed to be proportional to the amount of water mixed in the system.

  In addition, when Zn, Mg and Zn-Mg alloy are applied to the actual tank, pitting corrosion can be more efficiently achieved by applying a metal after forming a recess at the bottom of the tank so that water can easily collect. It became clear that it could be suppressed.

<About post-treatment films, etc.>
Next, a further study was conducted on the post-treatment film that can be applied on the plated layer or small block of the plated steel sheet as described above.
First, for the post-treatment film mainly composed of Cr ³⁺ described above, even better results were obtained when a post-treatment film having an adhesion amount of 5 to 40 mg / m ² per side in terms of Cr was applied. When the adhesion amount in terms of Cr was less than 5 mg / m ² , the corrosion resistance of the plated steel sheet as described above could not be further improved. Moreover, when the adhesion amount in Cr conversion exceeded 40 mg / m < ² >, the sliding resistance at the time of a process became high, and the workability of the above plated steel sheets was not able to be maintained.

  Further, the chemical conversion treatment layer is formed using a treatment liquid that does not contain environmentally harmful hexavalent chromium, such as a treatment liquid containing a salt of Zr or Ti, or a treatment liquid containing a silane coupling agent. It is also possible.

In these chromate-free treatments, a chromate-free treatment layer (chemical conversion treatment layer) containing no chromium and containing mainly Ti, Zr, P, Ce, Si, Al, Li, or the like is formed. The adhesion amount of the chromate-free treatment layer is preferably 10 to 1000 mg / m ² . When the adhesion amount of the chromate-free treatment layer is less than 10 mg / m ² , a sufficient rust prevention effect that further improves the corrosion resistance of the plated steel sheet cannot be obtained. Moreover, when the adhesion amount of a chromate free process layer exceeds 1000 mg / m < ² >, a rust prevention effect will be saturated and it will become expensive economically.

(About the fuel tank according to this embodiment)
As a result of further studies based on various findings obtained as described above, the present inventors have conceived a fuel tank according to an embodiment of the present invention described below. The fuel tank according to the present embodiment exhibits good corrosion resistance even when a deteriorated fuel or a factor that makes the corrosive environment in the fuel tank extremely severe like sludge enters from the outside, and is plated. It is a fuel tank with good perforation resistance and corrosion product resistance capable of suppressing the formation of corrosion products due to wear.

The fuel tank according to this embodiment includes a plating layer made of Sn-based plating having a composition of Sn- (5 to 40% by mass) Zn or Al-based plating having a composition of Al- (8 to 12% by mass) Si. A fuel tank made of a plated steel sheet having a plating layer adhesion amount of 20 to 50 g / m ² per side, and a position on the inner surface side of the fuel tank at the bottom of the fuel tank And a bottom member containing at least one of Zn, Mg, or a Zn—Mg alloy and having a K value given by the above formula (1) of K ≧ 0.030.

  Here, the base material of the plated steel sheet is not particularly limited, and a commonly used ultra-low carbon steel (for example, IF steel, ultra-low carbon steel containing Ti, Nb, etc.) is used. Is possible. It is also possible to use a steel plate to which appropriate amounts of Si, Mn, and P elements are added as reinforcing component elements, a steel plate to which B is added as a grain boundary reinforcing element, and the like.

  Moreover, when it is used outdoors and severe conditions regarding end face rust generation are assumed, it is possible to use a steel material containing Cr such as stainless steel.

  Moreover, the plating layer located on the base material is Sn-based plating having a composition of Sn- (5 to 40% by mass) Zn or Al-based plating having a composition of Al- (8 to 12% by mass) Si. A plating layer made of Here, the Zn content in the Sn-based plating is more preferably 6 to 20% by mass. Further, the Si content in the Al-based plating is more preferably 8 to 12% by mass.

  The method for forming the plated steel sheet having the plating layer as described above into a desired fuel tank shape is not particularly limited, and known processes such as a mechanical press, a hydraulic press, a counter hydraulic press, etc. It is possible to use the method.

  Further, at the bottom of the fuel tank, the bottom member as described above is provided on the plating layer on the inner surface side of the fuel tank. Such a bottom member may be realized by fixing a member made of the above composition component to the bottom of the fuel tank by a known method, or may be painted or sprayed with the above composition component. Thus, it may be formed at the bottom of the fuel tank. The fuel tank normally has a structure in which fuel is accumulated at the bottom, and the bottom member is made of metal and is naturally disposed at the bottom. Therefore, the fuel tank can be directly disposed without being particularly fixed.

  Here, the bottom of the fuel tank in which the bottom member as described above is disposed includes a bottom surface of the fuel tank, and ranges from the bottom surface to a predetermined height toward the top of the fuel tank. The height at which the bottom member is provided is not particularly limited, and may be set as appropriate depending on how much deteriorated fuel is expected to accumulate in the fuel tank.

  In the case where the bottom member as described above is realized by fixing the member composed of the composition component as described above, the bottom member may be fixed to the bottom portion on the inner surface side of the fuel tank by a known method. That's fine. The fixing method of the bottom member is not particularly limited, and may be fixed with an adhesive using a resin such as acrylic or epoxy, or an accessory such as a sub tank installed at the bottom of a normal fuel tank. You may attach in the bottom vicinity. In addition, when a bottom member as described above is realized by painting or spraying the above-described composition components, a known method such as coating or spraying can be used.

Further, on the plated steel plate and the bottom member, a coating layer mainly composed of Cr ³⁺ and having an adhesion amount of 5 to 40 mg / m ² in terms of Cr, or at least Ti, Zr, P, Ce, Si, Al, or Li You may further provide the chemical conversion treatment layer which does not contain chromium which has any one as a main component, and the adhesion amount is 10-1000 mg / m < ² >. Here, the adhesion amount of the coating layer is more preferably 10 to 30 mg / m ² in terms of Cr, and the adhesion amount of the chemical conversion treatment layer is more preferably 50 to 500 mg / m ² .

  By having such a configuration, the fuel tank according to the present embodiment exhibits good corrosion resistance even when a factor that makes the corrosive environment in the fuel tank extremely severe enters from the outside, and is accompanied by plating wear. It becomes possible to suppress the formation of corrosion products.

  In addition, when specifying content of each element in the plating layer with which the plated steel plate is provided and content of each element in the bottom member after manufacturing the fuel tank, for example, the amount of plating adhesion is measured by fluorescent X-ray analysis. A method (conforming to JIS G3314) or a method for measuring the amount of film adhesion may be performed in accordance with the measurement method.

  The fuel tank according to the present invention will be specifically described below with reference to examples. The following embodiment is merely an example of the fuel tank according to the present invention, and the fuel tank according to the present invention is not limited to the following example.

  In the examples shown below, the fuel tank was formed using an ultra-low carbon steel plate (IF steel plate) as a base material of the plated steel plate. Various plating was performed on the base steel sheet by the following method to form a plating layer.

(Formation of plating layer)
<Sn—Zn plating>
A plating layer made of Sn—Zn plating was formed on the base steel plate by the flux method. The flux was used by applying a ZnCl ₂ aqueous solution in a roll, and a 50 mass% flux in terms of Cl amount was applied at 50 g / m ² per side in terms of Cl amount.

The composition of the hot dipping was adjusted in the range of 0 to 60% by mass of Zn with respect to Sn. The immersion time was 8 seconds, and the plating adhesion amount was adjusted to 10 to 60 g / m ² per side by a wiping method after plating.

<Al-Si plating>
The plating layer made of molten Al—Si plating was formed by using a non-oxidation furnace-reduction furnace type line, adjusting the plating thickness by a gas wiping method after plating, and then cooling by gas cooling. The plating bath was obtained by changing Al in the range of 0 to 20% by mass to Al. Considering the dissolution of Fe from the steel sheet, a saturated concentration of Fe (about 2%) was dissolved. After plating, the plating adhesion amount was adjusted to 10 to 60 g / m ² per side by a wiping method. The plating appearance was good with no plating.

<Electrical Zn plating and Electrical Zn-Ni plating>
For electro-Zn plating, a solution containing 250 g / L of Zn sulfate and 100 g / L of Na sulfate was used. In addition, the electro-Zn-Ni plating used a solution containing 180 g / L of Zn sulfate, 100 g / L of Na sulfate, and 250 g / L of Ni sulfate. Thereafter, for these solutions, the pH of the plating solution was adjusted to 1.2 by adding sulfuric acid. The adhesion amount of the plating layer was changed in the range of 10 to 60 g / m ² per side.

The following treatment films A, B, or C were formed on the four types of plated steel sheets produced, and used as test materials.
The treatment film A is mainly composed of Cr ³⁺ such as Cr nitrate, and a treatment liquid containing ascorbic acid, water-dispersible silica and phosphoric acid is used. ^2. After drying, Cr: Si: P in the coating was applied at a mass ratio of 1: 3: 2, and then dried at an atmospheric temperature of 240 ° C.
The treatment film B uses a treatment liquid containing Zr oxide, phosphoric acid, Ce nitrate, and water-dispersible silica, and is 300 mg / m ² per side of the entire surface of the steel sheet surface with a bar coater. After Zr: P: Ce: Si was applied so as to have a mass ratio of 5: 2: 1: 2, it was formed by drying at an atmospheric temperature of 180 ° C.
The treatment film C uses a treatment liquid containing Zr nitrate, Li nitrate, and water-dispersible silica, and a bar coater provides a total coating amount of 500 mg / m ² per side on the surface of the steel sheet. After drying, Zr: Li in the film: After providing Si so that it might become 6: 1: 2 by mass ratio, it formed by drying at the atmospheric temperature of 180 degreeC.
In any of the cases described above, the amount of film adhesion was adjusted by appropriately adjusting the solid content concentration of the treatment agent.

<Processability>
Using the above four types of plated steel sheets, a forming test was performed with a drawing ratio of 2.3 using a cylindrical punch having a diameter of 50 mm by a hydraulic forming tester. The wrinkle suppression pressure at this time was 500 kg / cm ² . The evaluation of formability was based on the following index. In the following indicators, grades Δ and ○ were regarded as acceptable.

[Evaluation criteria]
A: Molding is possible, and there is no cracking or peeling of the plating layer.
Δ: Molding is possible, but cracks occur in the plating layer and there is minute peeling.
X: Molding is possible, but a crack of 10 μm or more occurs in the plating layer, and the plating is also peeled off.

<Internal corrosion resistance (Generally deteriorated fuel condition)>
The four types of plated steel sheets were formed into a cylindrical cup shape of 50 mmφ. Also, for the purpose of improving the corrosion resistance, select the Zn, Mg, Ni, Cu, Sn, Cr, Co, cut out a certain amount from these bullion, so that the bottom of the tank is present in the water phase generated at the bottom of the tank The bottom member was fixed to the lowest place using resin. Details of the bottom member are as shown in Table 1. Furthermore, 10% by volume of water is added to the deteriorated gasoline treated by the deterioration method according to JIS K2287, and the formic acid concentration becomes 100 mg / L and the acetic acid concentration is 200 mg on the lower phase side after the two-phase separation. / L was adjusted to be deteriorated fuel. The cylindrical cup filled with the deteriorated fuel was allowed to stand at 45 ° C. for 1000 hours, and the pitting depth after 1000 hours was measured in the same manner as described above. Evaluation was based on the following indicators. In the following indicators, grades Δ and ○ were regarded as acceptable.

[Evaluation criteria]
○: No pitting corrosion Δ: Pitting depth less than 20 μm ×: Pitting depth 20 μm or more

<Corrosion-resistant product properties>
The four types of plated steel sheets were formed into a cylindrical cup shape of 50 mmφ. Also, for the purpose of improving the corrosion resistance, select the Zn, Mg, Ni, Cu, Sn, Cr, Co, cut out a certain amount from these bullion, so that the bottom of the tank is present in the water phase generated at the bottom of the tank The bottom member was fixed to the lowest place using resin. Details of the bottom member are as shown in Table 1. Furthermore, the deteriorated gasoline processed by the deterioration method based on JISK2287 was prepared. 10% by volume of water is added to the deteriorated gasoline, and the lower phase side after two-phase separation is adjusted with a reagent so that the formic acid concentration becomes 100 mg / L and the acetic acid concentration becomes 200 mg / L. And deteriorated fuel. Thereafter, the obtained deteriorated fuel was sealed in the molded cylindrical cup in the same manner as described above.

  After leaving at 45 ° C. for 50 hours, the gasoline inside was taken out of the 40 cc cup, and the vertical wall portion of the cup was exposed to the atmosphere, and further left at 45 ° C. for 200 hours. After 200 hours, 40 cc of gasoline was added so as to be equal to the initial amount. In this state, the mixture was further allowed to stand at 45 ° C. for 50 hours, and thereafter, the internal fuel was reduced in the same manner as in the previous time, and further allowed to stand at 45 ° C. for 200 hours. These operations were repeated four times, and the test was terminated when the total standing time reached 1000 hours.

  After the test was completed, the corrosion products floating in the corrosive liquid and the corrosion products adhering to the inner surface of the cup were weighed. The corrosion product in the corrosive liquid was weighed by filtering the fuel with PTFE filter paper. Moreover, the corrosion product adhering to the inside of the cup was weighed after carefully peeling with a vinyl scrubber. Both were taken as the amount of corrosion product generated per cup. Evaluation was based on the following indicators. In the following indicators, the scores Δ and ○ were regarded as acceptable.

[Evaluation criteria]
○: Corrosion product amount 0.01 g / cup or less Δ: Corrosion product amount 0.01 g / cup or more to less than 0.1 g / cup ×: Corrosion product amount 0.1 g / cup or more

<Internal corrosion resistance (deteriorating conditions)>
Using the above four types of plated steel sheets, a Monaca-type tank having an internal volume of 40 liters was formed. In addition, for the purpose of improving corrosion resistance, choose Zn, Al, Mg, Ni, Cu, Sn, Cr, Co, cut out a certain amount from these bullion, so that it exists in the water phase generated at the bottom of the tank, A bottom member was obtained by fixing the resin at the lowest place on the bottom of the tank using a resin. Details of the bottom member are as shown in Table 1. 100 cc of water is added to 38 liters of deteriorated gasoline in the molded tank, and the formic acid concentration is 1000 mg / L and the acetic acid concentration is 2000 mg on the water phase side existing in the lower phase separated into two phases. / L was adjusted using a reagent to obtain a highly deteriorated fuel. Thereafter, the obtained highly deteriorated fuel was sealed in the molded tank.

  The tank was allowed to stand at 45 ° C. for 1000 hours, and the pitting depth after 1000 hours was measured in the same manner as described above. Evaluation was based on the following indicators. In the following indicators, grades Δ and ○ were regarded as acceptable.

[Evaluation criteria]
○: No pitting corrosion Δ: Pitting depth less than 20 μm ×: Pitting depth 20 μm or more

<Internal corrosion resistance (addition of sludge)>
Using the above four types of plated steel sheets, a Monaca-type tank having an internal volume of 40 liters was formed. In addition, for the purpose of improving corrosion resistance, choose Zn, Al, Mg, Ni, Cu, Sn, Cr, Co, cut out a certain amount from these bullion, so that it exists in the water phase generated at the bottom of the tank, A bottom member was obtained by fixing the resin at the lowest place on the bottom of the tank using a resin. Details of the bottom member are as shown in Table 1. 100 cc of water is added to 38 liters of deteriorated gasoline in the molded tank, and the formic acid concentration is 100 mg / L and the acetic acid concentration is 200 mg / L on the aqueous phase side existing in the lower phase separated into two phases. It was adjusted with a reagent so as to be a deteriorated fuel. Furthermore, 20 g of FeOOH simulating sludge was added to the deteriorated fuel. Thereafter, the obtained deteriorated fuel was sealed in the molded tank.

  The tank was allowed to stand at 45 ° C. for 1000 hours, and the pitting depth after 1000 hours was measured in the same manner as described above. Evaluation was based on the following indicators. In the following indicators, grades Δ and ○ were regarded as acceptable.

[Evaluation criteria]
○: No pitting corrosion Δ: Pitting depth less than 20 μm ×: Pitting depth 20 μm or more

<Comprehensive evaluation>
The prepared samples were comprehensively evaluated by comprehensively evaluating the above-mentioned three viewpoints of the three types of inner surface corrosion resistance, workability, and corrosion resistance product properties. Evaluation was based on the following indicators. In addition, in the following indicators, the grades ○ ⁻ and ○ were regarded as acceptable.
[Evaluation criteria]
○: Excellent characteristics as a fuel tank. (Characteristics: all ○)
○ ⁻ : Has characteristics that can be used as a fuel tank. (Characteristics: ○, △)
X: Not suitable for use as a fuel tank. (X is in the characteristics)

  The obtained results are summarized in Table 1 below.

  As is apparent from Table 1 above, with respect to all items of the plating composition and the amount of adhesion, the type and amount of the bottom member that mildens the corrosive environment, Invention Examples 1 to 19 that satisfy the conditions of the present invention are workability, Good characteristics were exhibited for all items of internal corrosion resistance under general deteriorated fuel conditions, corrosion product resistance, internal corrosion resistance under poor conditions, and internal corrosion resistance with sludge addition.

  On the other hand, Comparative Example 1 having a low Zn content in the Sn—Zn plating layer had good workability and corrosion resistance product properties, but had insufficient inner surface corrosion resistance under all conditions. Moreover, although the comparative example 2 with high Zn content in a Sn-Zn plating layer had favorable workability and internal corrosion resistance, corrosion of Zn progressed by air | atmosphere and resulted in inferior corrosion-resistant product property. Furthermore, Comparative Examples 3 and 4 with a small amount of Sn—Zn adhesion had insufficient inner surface corrosion resistance under all conditions. Moreover, although the comparative example 5 with much Sn-Zn plating adhesion amount had favorable corrosion resistance and corrosion-resistant product property, it resulted in inferior workability.

  Comparative Examples 6 and 7 having a low Si content in the Al—Si plating layer and Comparative Examples 8 and 9 having a high Si content in the plating layer both resulted in poor workability. Moreover, the comparative example 10 with few adhesion amounts of Al-Si plating had inadequate internal surface corrosion resistance on all the conditions. Further, Comparative Example 11 having a large amount of Al-Si plating adhered had good corrosion resistance and corrosion resistance, but had poor workability.

  Moreover, even if the plating composition and the amount of adhesion of the plating layer are within an appropriate range, Comparative Examples 12 and 13 with a small amount of Zn applied to the tank and Comparative Examples 14 to 19 with an inappropriate metal applied to the tank. The result was inferior to the internal corrosion resistance under poor conditions and sludge addition conditions.

  Furthermore, since Comparative Example 20 using Zn for the plating layer was fundamentally lacking in corrosion resistance of plating, it was rejected in all items other than workability. Moreover, although the comparative example 21 which used Zn-Ni for the plating layer was able to ensure corrosion resistance, it resulted in inferior corrosion-resistant product property.

The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

Claims (3)

It has a plating layer made of Sn-based plating having a composition of Sn- (5 to 40% by mass) Zn or Al-based plating having a composition of Al- (8 to 12% by mass) Si, and the plating per one side A fuel tank made of a plated steel sheet having a layer adhesion amount of 20 to 50 g / m ² ;
At the bottom of the fuel tank, it is located on the plating layer on the inner surface side of the fuel tank and contains at least one of Zn, Mg, or Zn—Mg alloy, and is given by the following formula (1) A bottom member having a K value of K ≧ 0.030;
A fuel tank.

K = Zn (g) /65.4+Mg (g) /24.3 ... Formula (1)

Here, in the above formula (1),
Zn (g): Zn content in the bottom member (unit: g)
Mg (g): Mg content in the bottom member (unit: g)
It is.   The fuel tank according to claim 1, wherein the contents of Ni, Fe, Co, and Cu in the bottom member are each 0.5 mass% or less. On the plated steel sheet and the bottom member, a coating layer mainly composed of Cr ³⁺ and having an adhesion amount of 5 to 40 mg / m ² in terms of Cr, or at least Ti, Zr, P, Ce, Si, Al, or Li 3. The fuel tank according to claim 1, further comprising a chemical conversion treatment layer containing any one of the main components and not containing chromium and having an adhesion amount of 10 to 1000 mg / m ² .

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